$\begingroup$You guessed it, what's in the question does not match your definition. My bets are on a typo.$\endgroup$
– fgrieuMay 15 '18 at 12:25

$\begingroup$Yes, I thought that might be the case, but as my mathematical ability is very basic, I did not want to presume anything. Thanks @fgrieu$\endgroup$
– PaulMay 15 '18 at 12:33

$\begingroup$In fact, the question cannot possibly be correct as stated (even if a different curve model had been introduced in class): That curve has genus $0$, hence is (by definition) certainly not an elliptic curve.$\endgroup$
– yyyyyyyMay 15 '18 at 15:11